Python GDAL/OGR: retrieved feature is NoneType

I’m doing some scripts in Python to deal with shapefiles, and I have an issue I don’t understand. I’m looping over a shapefile, and I want to retrieve the geometry of each feature, but very often I get an error saying:

    pointGeo = pointFeat.GetGeometryRef()
AttributeError: 'NoneType' object has no attribute 'GetGeometryRef'

Here’s the way I did it:

        for j in range(pointsLayer.GetFeatureCount()):
                pointFeat = pointsLayer.GetNextFeature()
                pointGeo = pointFeat.GetGeometryRef()
                if pointGeo.Within(whatever):
                    ...

I don’t think my shapefile is corrupted or damaged, as I tried with several… and I often get this error, but for some features I don’t get it.
Any idea how to solve this?

Thanks